Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator (basic and diluted):
Net income	$ 159,332	$ 148,439	$ 452,944	$ 384,685
Denominator:
Denominator for basic earnings per share - weighted-average shares	118,546	132,777	123,448	136,895
Effect of stock options	1,993	2,256	2,222	2,288
Denominator for diluted earnings per share - weighted-average shares	120,539	135,033	125,670	139,183
Earnings per share - basic	$ 1.34	$ 1.12	$ 3.67	$ 2.81
Earnings per share - assuming dilution	$ 1.32	$ 1.10	$ 3.60	$ 2.76